Field of the Invention
The invention relates to a fuel cell block and a method for adjusting the removal of inert gas from a fuel cell block having a number of fuel cells, in which a progressive increase in a proportion of inert gas in a gas mixture flowing through the fuel cells on a cathode or anode side is brought about.
In general, a fuel cell includes an electrically conductive current transformer plate, a cathode, an ion-conducting intermediate layer, an anode, and a further electrically conducting current transformer plate, which are stacked on one another in that order in the form of flat plates and form an electrolyte-electrode unit. In the case of a PEM fuel cell, the electrolyte-electrode unit is also called a membrane electrode unit, wherein PEM stands for polymer electrolyte membrane, or proton exchange membrane.
Fuel cells of such a structure are known, among other sources, from the Fuel Cell Handbook by Appelby and Foulkes, New York, 1989, and by the article by K. Strasser, entitled "Die alkalische Siemens-Brennstoffzelle in Kompaktbauweise" [The Siemens Compact Alkaline Fuel Cell], VDI Manual No. 0996, 1990, pp. 25-46. Since the fuel cell is capable of converting chemically bound energy directly into electrical energy, it makes it possible for fuels such as hydrogen, natural gas and biogas to be converted into electrical energy at greater efficiency and with less environmental burden than the previously known conventional internal combustion engines, having an efficiency which is limited by the so-called Carnot process, were capable of doing.
A fuel cell block is made up of alternatingly stacked-together electrolyte-electrode units, gas chambers, cooling units and pressure cushions. Seals and possibly spacers are built-in between those individual components. The spacers may be constructed as bipolar plates with intervening spring plates. The various liquid and gas chambers of the block are supplied from axial channels through radial channels that extend through the seals. Such an axial channel extends at right angles to the plane of the stacked-together plate-like components of the fuel cell block. Such a radial channel extends correspondingly in the plane of the plates.
During operation of the fuel cell block, in particular with a block formed of PEM fuel cells, a problem arises, when the anode side is supplied with industrially pure water and the cathode side is supplied with industrially pure oxygen, which is that water, that is created in the fuel cells as a result of the electrochemical reaction of hydrogen and oxygen to make water, and inert gases such as nitrogen, carbon dioxide, and noble gases, which are contained in slight percentages as contaminants in industrially pure gases, must be removed from the fuel cells.
Heretofore, that problem was solved by regulating the inert gases as a function of the electric current and concentrating them in the flow direction of the gas mixture on the anode or cathode side. An unavoidable disadvantage which had to be tolerated was that major expense was needed for the circuitry on the high-current side. The high-current circuitry of such a fuel cell block is bulky, heavy and expensive, which argues against mass usage of the PEM fuel cell, for instance in electric vehicles.